POS0430 SYNOVIAL FLUID-DERIVED EXTRACELLULAR VESICLES FROM RHEUMATOID ARTHRITIS AND OSTEOARTHRITIS MODULATE DIFFERENT HIPPOCAMPAL SYNAPTIC ACTIVITIES

Abstract

BackgroundAccumulating evidence suggests that poor mental health is one of the most common comorbidities of both rheumatoid arthritis (RA) and osteoarthritis (OA) [1]. Even if underpinning RA and OA are different genetic, structural, mechanical, and immunologic pathways involved in their pathogenesis, poor mental health, and joint involvement are intertwined and negatively affect their mutual course by contributing to global disability. Thus, new insights into mechanisms that link these disorders are needed to identify new actionable biomarkers to drive more personalized therapeutic strategies. Amidst potential mediators, extracellular vesicles (EVs) play a central role in terms of communication between cells, they cross the blood-brain barrier and based on their cargos can affect the recipient cell function [2].ObjectivesTo isolate EVs from synovial fluid (SF) in RA and OA patients and to evaluate if and how these EVs can alter in vitro synaptic transmission of murine hippocampal neurons.MethodsIn this cross-sectional pilot study, consecutive adult RA and primary OA who were referred to the Rheumatology Unit for aspiration of joint effusion were enrolled. Demographic and clinical variables and mental health rating scales were collected. Discarded SF were collected and EVs were isolated and analyzed by Malvern NanoSight NS300 system to obtain information on their number and size. Afterwards, DIV14 cultured wild-type hippocampal neurons were exposed for two hours to OA- and RA-EVs at low and high concentration EVs. Thus, miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs), which reflects glutamatergic and GABA-ergic activity respectively, were examined by exploiting patch-clamp recordings in the whole-cell configuration. Frequency and amplitude were analyzed to evaluate potential changes at the presynaptic or postsynaptic compartment. Mann Whitney test was used to compare two different samples.ResultsEight RA patients (7 female, mean age 57 yrs), and 5 primary OA (4 female, mean age 60 yrs) were recruited for SF aspiration. The mean VAS pain was 7.25 in RA and 6.5 in OA. No statistically significant differences were found between the two groups in mean rating scale scores although patients affected by RA had more severe depressive symptoms (Montgomery Asberg Depression Rating Scale -MADRS- means scores: 16.57) with respect OA group (MADRS mean scores: 10). The Nanoparticle tracking analysis showed that RA-EVs were significantly more in number compared to OA-EVs (Figure 1 A), mimicking more inflammation, while no significant difference in size was observed. Analysis of miniature events revealed the occurrence of two different changes. High concentration of OA-EVs has led to an increased amplitude of excitatory events, meaning an increased susceptibility of neurons to glutamate in the post-synaptic compartment (Figure 1 B). Whereas low concentration of RA-EVs has led to a decreased frequency of inhibitory events, which reflects a reduced function of GABA-ergic synapse in the pre-synaptic compartment (Figure 1 C).Figure 1.ConclusionOur results suggest that SF-derived EVs from OA and RA patients lead to different specific changes of neurotransmission, with different concentration needed to alter neuronal spontaneous activity in post-synaptic and pre-synaptic compartment, respectively. EVs may provide insight into the pathogenesis of joint-brain communication in RA and OA, unraveling specific pathways thus allowing targeted therapies for neuropsychiatric involvement.